A strong earthquake under the ocean off Indonesia's Sumatra and Nias islands has caused some panic but no damage or injuries.

The U.S. Geological Survey gave a preliminary estimate of the strength of the Tuesday morning quake at 6.7 on the Richter scale, and said the epicenter was close to the island of Nias. The quake did not cause a tsunami.

An earthquake in late March killed more than 900 people on Nias.

Both Sumatra and Nias have experienced countless earthquakes since a massive tsunami-producing quake on December 26.

The latest official death toll from that tragedy stands at some 176,000 people killed -128,000 of them in Indonesia. Nearly 50,000 people are still listed as missing, but most of them are feared dead.